The objective of the proposed research is to characterize the collagenolytic proteases involved in the metabolic breakdown of collagen and to explore the role of steroid hormones in regulating this breakdown. These studies involve the involuting rat uterus, an organ that shows extremely rapid breakdown of collagen. Collagenase activity can be demonstrated to change in parallel with the rate of collagen breakdown and both parameters are reduced equally by estradiol treatment. It is proposed to study the phenomenon of collagenase latency, to prove that this is due to an enzyme-inhibitor complex and to identify the inhibitor, if possible. A serine proteinase of the uterus is able to activate latent collagenase and may represent an important control enzyme. A second latent metalloprotease of the uterus digests Azocoll and gelatin; it may be a gelatinase acting in sequence after collagenase. Intracellular digestion of collagen is important in the uterus. Two novel collagenolytic cathepsis may be involved in this lysosomal process. All of the above-mentioned proteases will be purified and characterized. To support the hypothesis that these enzymes play a role in collagen breakdown, attempts will be made to show that their activities vary in parallel to changes in the rate of collagen breakdown. Agents that inhibit collagen breakdown such as estradiol, progesterone, cytochalasin B, triamcinolone, and diethylstilbestrol will be tested for parallel inhibition of enzyme activity. An understanding of the processes of collagen breakdown and their possible pharmacological control by hormone treatment would be of wide interest in reproductive biology (follicle rupture, cervical ripening), developmental biology (embryo morphogenesis, skeletal remodeling), and pathology (cancer invasion, arthritides, gingivitis, etc.).